In order to rise efficiency of the wastewater treatment in a refinery plant, several oxidation experiments were done, testing their applicability as an additional pretreatment method. The influence of treatment with low concentrations of H 2O 2 combined with stirring and UV light on degradation of organic compounds present in the refinery wastewater was studied. Oxidation of the total petroleum hydrocarbons occurs at relatively low concentrations of H 2O 2, additional UV irradiation slightly accelerates the process due to the increased formation of hydroxyl radicals. 1,2-dichloroethane and t-butyl methyl ether degrade in the similar manner and except for the lowest H 2O 2 concentration used (1.17 mM), the reduction after 24 h is total. The degradation rate for dichloromethane is the lowest one, depending both on hydrogen peroxide concentration and the presence of UV. Its maximum reduction of 83% was obtained using the highest applied peroxide concentration of 11.76 mM.